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The restoration of the ruins of the Abbey-Tower in the city centre of Sint-Truiden in Belgium is presented as an example of the tedious and comprehensive task involved in all restoration or rehabilitation projects, where the extra cost of the restoration must be justified by the added value connected with the conservation of authenticity and with the contribution to sustainable development. The development and evolution of the project took 28 years, between the damages caused by the fire in 1975 and the start of the restoration in 2003. Since 2004, the restored ruin started a new life as a beacon of the city of Sint-Truiden, highly appreciated by tourists as well as by the inhabitants.

The restoration of St Martin church started end of the 1990’s by lacing-up the building with stabilizing steel frames. The layout of the lacing-up frames was inspired by the assumption that the observed cracks and deformations in the building were caused by differential settlements of the foundations. Further investigations during the final restoration works in 2011–2012 revealed that cracks were caused by inappropriate foundation interventions as part of an earlier restoration project in 1949–1950 as well as by non-balanced forces from the vaults. Based on the new findings the global restoration concept was adapted and strongly simplified.

The polychrome mosque of Sharaf Al-Din in the historic center of Cairo dates back to (717–738 ah ) (1317–1337 ad ). It consists of different layers of red brick and yellow limestone, characteristic of Mamluk architecture; the building is currently below the street level. The study concentrated on the mineralogical and physicochemical composition of these two construction materials, as well as identifying the Mokattam quarry as the source for the limestone. Furthermore, the presence of efflorescence in specific locations of the building was noted, and their composition was analyzed to identify the main soluble salts; these were found to be halite, gypsum and ettringite, the former two on limestone ashlars, and the latter on brick boundaries. Their formation and their possible different origins are discussed.

This article reviews the carbonation process through biomineralization referred to as Microbial Induced Calcium Carbonate Precipitation (MICCP) for the conservation of carbonate stone monuments and historic building materials. This biological process widely occurs in nature as microbes produce inorganic materials within their basic metabolic activities. The first patent, which explained this method dates from approximately twenty-five years ago. Since then, different research groups have investigated substitute methodologies and various technical applications to provide a protective calcium carbonate layer on the surface of deteriorated historic buildings and stone monuments as well as to consolidate their inner weakened structure through this biodeposition process. The article reviews selected literature, highlights open queries and promotes discussion of a selection of issues, production mechanisms, application techniques, performance and bonding with stone structure. While many questions regarding this significant method have been focused in published sources, there are considerable possibilities for new research.